In general, a water-based ink ballpoint pen has such a low viscosity as 50 mPa·sec to 3 Pa·sec while a ballpoint pen using an oil-based ink having a similar structure has an ink viscosity of 3 Pa·sec to 20 Pa·sec, and therefore when the pen is left standing upward or horizontally, the ink leaks in a certain case. Further, the ink is likely to be scattered by slight impact to stain hands and cloths, and in order to prevent this, an ink follower is installed at a plug part in an ink reservoir of a water-based ink ballpoint pen.
A lot of ink followers which are increased in a viscosity by blending a base oil with a viscosity-controlling agent such as silica, metallic soap, a clay thickener and a thermoplastic elastomer has so far been applied as the above ink follower (for example, Japanese Patent No. 3016749).
However, if such ink followers are used particularly for a water-based ink ballpoint pen for bold lines consuming a large amount of inks, brought about are the problems that starving of the drawn lines is caused in writing because of difficulty in following of the ink and that a part of an ink follower adheres and remains on the inner wall of an ink reservoir in consuming the ink to result in causing a shortage in the ink follower in writing so that the ink flows backward or that an ink discharge amount in writing becomes instable due to an influence of the shortage in the ink follower. In the ballpoint pens of specifications other than those for bold lines, the same problems are brought about in a certain case when the writing speed is increased.
Such problems are considered to originate in a slower following speed of an ink follower than an ink-consuming speed.
Further, in an ink follower in which a viscosity value is controlled to a lower level in order to improve the above problems, brought about are the problems that the follower and the ink are scattered when impact is given to the pen body and that the ink follower leaks out from the ink reservoir when the pen is stored at a high temperature with the pen tip turned upward.
In light of the conventional problems described above, the present invention intends to solve them, and an object thereof is to provide an ink follower for a water-based ink ballpoint pen which has stable followability regardless of a pen specification, an ink discharge amount in writing and a writing speed and which does not cause back leaking of the ink originating in a shortage in the ink follower in writing and is not scattered by impact given to the pen body and which does not leak out from the ink reservoir in storing the pen at a high temperature. It is a matter of course that the above ink follower is an ink follower for a water-based ink ballpoint pen which can prevent the ink from volatilizing by shutting off the ink from the outside air (volatilization preventing property) and which can prevent the ink from leaking in writing with the pen turned upward.